In electrostatography an image comprising a pattern of electrostatic potential (also referred to as an electrostatic latent image) is formed on an insulative surface by any of various methods. For example, the electrostatic latent image may be formed electrophotographically (i.e., by imagewise radiation-induced discharge of a uniform potential previously formed on a surface of an electrophotographic element comprising at least a photoconductive layer and an electrically conductive substrate), or it may be formed by dielectric recording (i.e., by direct electrical formation of a pattern of electrostatic potential on a surface of a dielectric material). Typically, the electrostatic latent image is then developed into a toner image by contacting the latent image with an electrographic developer. The toner image is usually transferred from the element directly to a receiver such as paper, or to an intermediate transfer member, and from the intermediate transfer member to a receiver. Typically, the toner is fused to the receiver through pressurized contact with a heated fuser member.
In normal use, each of the surfaces onto which the toner is contacted must be smooth and of uniform thickness. Toner contacting surfaces include, for example, the surfaces of the photoconductive element or insulative member, the intermediate transfer member and the fuser member. The surfaces must be smooth and of uniform thickness to provide for transfer of all the toner from one member to the next or from one member to a receiver without leaving relief marks in the final toner image of a nonuniform surface from which the toner was transferred.
Many transfer materials are known in the prior art for the surface layers of the members in an electrostatographic machine. The most common are silicone rubbers, polyurethanes, fluoropolymer resins or fluoroelastomers. See, for example, U.S. Pat. Nos. 3,893,761; 4,453,820; 3,923,392; 4,455,079; 4,068,937; or 3,697,171 which disclose specific examples of suitable materials.
Commonly, electrostatographic rollers are constructed of a core onto which the layers of polymers, such as silicone rubber, polyurethane, or fluoroelastomers, are compression molded and then ground to achieve a closer approximation to a cylinder. There are mechanical deficiencies associated with this approach, in that the compression molding leads to non-uniform thickness and the grinding imparts a surface roughness, which results in a visible pattern in the transferred toner image. For very high image quality, coated members having very uniform thickness and very smooth surface texture are desired.
Electrostatographic belts have been made by solvent-coating or extrusion-coating a polymeric sheet cutting to size and splicing the ends together. Solvent-coating is undesirable, because the capture of the evaporating solvent is difficult. Extrusion-coating is undesirable, because it does not produce belts having smooth coatings of precise thicknesses without additional grinding steps.
Therefore, there is a need in the art for methods of making parts which provide belt or roller surfaces which are very smooth and of uniform thickness.